Varifocal objective

ABSTRACT

A varifocal objective with a zoom range of about 1:1.8 or 1:1.9 consists of a fixed positive front component, a fixed positive rear component and a single axially shiftable negative intermediate component. The front component consists of a biconcave first lens and closely spaced positive second and third lenses, these latter lenses being separated from the first lens by a large air space nearly equal to half the overall axial length of that component. The intermediate second component is a single biconcave lens. The rear component consists of five airspaced lens members of which the first, second, third and fifth members are positively refracting singlets, the negatively refracting fourth member being either a doublet or singlet.

United States Patent [191 Muszumanski Dec. 23, 1975 VARIFOCAL OBJECTIVE [75] Inventor: Trude Muszumanski, Vienna,

Austria 22 Filed: Dec.28, 1973 21 Appl. No.:429,696

[30] Foreign Application Priority Data .Ian. 3, 1973 Austria 45/73 [52] US. Cl 350/184; 350/186 [51] Int. Cl. G02B 15/00 [58] Field ofsearch 350/184, 186

[56] References Cited UNITED STATES PATENTS 3,346,320 10/1967 Macher 350/184 3,350,155 10/1967 Macher................ 350/184 3,556,641 1/1971 Takahashi 350/184 3,715,151 2/1973 Muszurnanski et al. 350/184 Primary Examiner-Edward S. Bauer Assistant Examiner-Conrad J. Clark Attorney, Agent, or Firm-Ernest G. Montague; Karl F. Ross; Herbert Dubno [57] ABSTRACT A varifocal objective with a zoom range of about 1:1.8 or 1: 1.9 consists of a fixed positive front component, a fixed positive rear component and a single axially shiftable negative intermediate component. The front component consists of a biconcave first lens and closely spaced positive second and third lenses, these latter lenses being separated from the first lens by a large air space nearly equal to half the overall axial length of that component. The intermediate second component is a single biconcave lens. The rear component consists of five air-spaced lens members of which the first, second, third and fifth members are positively refracting singlets, the negatively refracting fourth member being either a doublet or singlet.

5 Clairm, 4 Drawing Figures fmin fg min U.S. Patent Dec. 23, 1975 Sheet 2 of2 3,927,931

VARIFOCAL OBJECTIVE FIELD OF THE INVENTION on the side of the short conjugated, and a negative intermediate component which is axially slidable between the front component and the base lens assembly.

PRIOR ART Conventional varifocal objectives of the type referred to above, with but a single axially shi-ftable component, suffer from the disadvantage that the brightness on the outermost image edge is reduced to 30 percent with respect to the brightness in the center of the image. Moreover, the structural length of the. lens elements which constitutes the varifocal system amounts to more than 1.7 times the maximum focal length of the zoom objective. The structural length mentioned above refers to the constant distance between the front and rear components if all the components are assumed to consist of infinitely thin lenses.

OBJECT OF THE INVENTION The object of the invention is the provision of an improved varifocal or zoom objective capable of being relatively cheaply manufactured and providing an improved overall performance as compared with prior-art zoom objectives of the type described.

SUMMARY OF THE INVENTION In accordance with my present invention, the axially fixed front component of a varifocal objective of the general type described above consists of a negative first lens, a positive second lens, and a positive third lens closely spaced from the second lens, the first lens being separated from the second lens by an air space which is substantially greater than the spacing of the second and third lenses and which preferably equals close to half the axial length of this front component. The shiftable intermediate component is a single negative lens whereas the rear component consists of a plurality of positive lens members and an interposed negative lens member.

Advantageously, the negative lenses of the front and intermediate components are biconcave, the second lens of the front component being biconvex while the third lens thereof is nearly planoconvex with an almost flat rear surface. The lens members of the rear comp0- nent may be, from front to rear, two biconvex positive singlets, a meniscus-shaped positive singlet, a biconcave lens member which may be either a doublet or a singlet, and another biconvex singlet. I have found that the relatively large distance between the first and second lenses of the first component, which may substantially exceed the diagonal of the image format 2y, provides a particularly advantageous correction combined with a short structural length. There is also the advantage that the brightness at the outer image edge amounts to more than 40 percent of the brightness in the image center, in a system having a relative aperture of l:l.2, while maintaining a correction which is characterized by high contrast over the entire image field and the entire zoom range. Another advantage of my 2 improved varifocal objective is that it consists of a relatively small number of lenses which can be produced from relatively inexpensive kinds of glass.

BRIEF DESCRIPTION OF THE DRAWING The invention will now be described in more detail, by way of example, with reference to the accompanying drawing in which:

FIG. 1 shows diagrammatically an axial section through a varifocal objective according to my invention, intended for a film projector (not shown) in a position of minimum overall focal length;

FIG. 2 illustrates the components of the objective in their setting for an intermediate overall focal length;

FIG. 3 shows the components in their position of maximum overall focal length; and FIG. 4 shows a modified varifocal objective in the maximum-focallength position.

The varifocal objective shown in FIGS. 1 3 comprises ten lenses L L Lenses L L and L 0 are singlets whereas lenses L and L, are cemented to each other to form a cemented lens member comprising a so-called abnormal glass pair", i.e., a doublet wherein the more strongly refractive (here negative) lens has the higher Abbe number in contrast to the normal practice.

As is apparent from FIG. 2, the lenses L L form three distinct components I, II and III. The first component 1 consists of axially fixed lenses L L with lenses L and L separated by an air space d slightly greater than half the axial length d +d,+d +d.,+d of this component as will be apparent from the numerical values given below. The intermediate component II consists of the negative lens L which is slidable along the optical axis; the rear component III comprises a positive base lens assembly which is rigidly coupled to the positive front component 1.

FIGS. 1, 2 and 3 show the same ten-lens system in three different positions, i.e. with minimum overall focal length f intermediate overall focal length f and maximum overall focal length f In FIG. 4 I have illustrated a modified system with only nine lenses L 11,, the doublet L,;, L, being replaced by a singlet L',,.

In the following Tables I and II I have given representative numerical values for the radii r, r, and the thicknesses and separations d d of the lenses L L of FIGS. I 3, based upon a numerical value fmin I, together with the refractive indices n and the Abbe numbers 11,, thereof, for two different examples; Table III represents corresponding values for the radii r r' and the thicknesses and separations d d as well as the refractive indices n and the Abbe numbers 11 for the lenses L, L, of FIG. 4.

3 4 TABLE l-continued TABLE 111 Thicknesses Thicknesses Lenses Radii and Separations n, v Lenses Radii and Separations n u,

0.282..f,,,,, I d, 0.673 r, 6.239 5.600 I L, 6, 0.187 1.589 61.3 1 1 -24 1 -1a.91s l0 [0000 920 d 0.008 r. I 1.. 2.024 I 4516 d. 0.003 r fling d.l 0.273 1.641 601 1 0240 60.3

d 0.008 I .620 r +1000 r. 124.416 0 (Mr L-, 6., 0.398 1.641 60.1

4847 d" 0M3 r7 (L 2.4241, r, 1 1 L 1 11.. 0.339 1.720 50.4 623 6 r 3604 d1. 0.078 1.699 30.1 2.7691 i 1' a' md 0.183 0449.1... 1,, 1.292 r, 8.026 L, d 0.296 1.717 48.0 0,192 61.3

is .589 m L753 1... 54.640

d 0.016 m= L000 1.. 2.224 Raf L, d 0.232 61.3 Relative Aperture 1:1.2 5g9 2y =0.523 1,, 8.997

d 0.052 r 0.912 L d 0.384 61.3 TABLE 11 89 r 10.194 Thlcknesses (H44 Lenses Radii and Separations n v, r. 6.215

r 240 a d 0.420 805 25.4 L 6. 0.156 1.618 49.8 0536 r, 3.990 6., 0.240 0-656 1., 0.825 r, 4.680 L, 11,, 0.304 L, d, 0.234 1.620 60.3 69

d, 0.008 r, 4.963 f 1.000 L, d, 0.234 1.620 60.3 m; 1-

121 30 Relative A erture 1:1.2

0.1021,,I 2y 052 d.

2.3641,...- 5.821 1 The 1nd|v1dua| focal lengths f,, f and f, of compo- L4 3 7M 0109 L623 nents 1, l1 and 111 can be calculated from the foregoing 2.7004, values as follows:

0438.1]...I r, 7.825 I v 1 f," r 700 5o TABLEI +7.89 3.67 +1.46 d 0 008 TABLE 11 +7.81 3.66 +1.50 t 2 I52 TABLE 111 +7.96 3.76 +1.56

ll L. d 0.273 1.641 60.1

1., 12.932 n 0 952 0008 which corresponds, approximately, to a ratio of +5.5

11 l3-9l6 In all of the dimensions iven in the above three 11 0 117 8 I 6006 examples the following tolerances are to be assumed to L, d 0.351 1.720 50.4 apply a deviation of the curvature of individual surfaces 0-429 by up to t 10 percent of the refractive power of the L, d 0.078 1.699 30.1 0

r" 0503 6 correspondmg lens element; a devtatton of the thickd 0.246 nesses of up to i 10 percent of the focal length of the H04 corresponding lens element, a deviation of the refrac- L d 0.312 1.720 50.4

rm L931 t1ve numbers of up to t 0.03 and of the Abbe numbers 1,...,,= 1.000 of fin? 25 1 61311111 I l I 1 16111111 651; erture 111.2 1. A vanfocal objective c0ns1st1ng of a fixed posltlve front component, an axially shiftable negative intermediatecomponent and a fix? positive rear component;

said front component consisting of a biconcave first lens, a biconvex second lens, and a'nearly planoconvex third lens closely spaced from said second lens, said first lens being separated from said second lens by an air space close to half the axial length of said front component; said intermediate component being a single negative lens; said rear component consisting, from front to rear, of two biconvex positive lens members, a meniscus-shaped positive lens member, a biconcave lens member and another biconvex lens member; the individual focal lengths of said front component, said intermediate component and said rear component being approximately related in the ratio +5.5 2.5 +1, the relative positioning of said components being such as to provide an image diagonal which is shorter than the separation of said first and second lenses.

2. A varifocal objective as defined in claim 1 wherein said positive lens members are singlets.

3. A varifocal objective as defined in claim 1 wherein the numerical values of the radii r, 1' and of the thicknesses and separations d, d of said first, second and third lenses L L L said single negative lens L said two biconvex lens members L L said meniscusshaped lens member L-,, two cemented lenses L L, constituting said biconcave lens member, and said other biconvex lens member L based upon a value of unity for the minimum overall focal length, their refractive indices n and their Abbe numbers 11,, are substantially as given in the following table:

Thicknesses Lenses Radii and Separations n, 1

r, 7.825 L, a, 0.156 41.9

d, 0.656 r, +4.673 14 d, 0.257 60.3

d, 0.008 +5.451 L, a. 0.211 60.3

2.519..f,,,,, r, 5.802 L. a, 0.109 55.2

0.2112..f,,. r, +6239 L. d, 0.187 61.3

.589 r -1s.91s

11,, 0.113 L, 4'847 d 0339 s04 4. A varifocal objective as defined in claim 1 wherein the numerical values of the radii r r and of the thicknesses and separations d, d of said first, second and third lenses L L L said single negative lens L said two biconvex lens members L,,, L,,, said meniscusshaped lens member L-,, two cemented lenses L L constituting said biconcave lens member, and said other biconvex lens member L based upon a value of unity for the minimum overall focal length, their refractive, indices 11,, and their Abbe numbers v,, are substantially as given in the following table:

Thicknessess Lenses Radii and Separations n,, 11,,

r, 6.240 L, d, 0.156 49.8

d, 0.656 r, 4.680 1. d, 0.234 60.3

0438.1 r, 7.825 L; d. 0.187 61.3

C1 0.003 1' 2.152 n d 0.273 60.1

11,, 0.001; r 0.952 L d 0.393 61.3

(1 0.117 I 6.006 L. d 0.351 50.4

d 0.246 d 0312 504 L M 5. A varifocal objective as defined in claim 1, wherein the numerical values of the radii r, 1'',,, and of the thicknesses and separations d, d' of said first, second and third lenses L,, L',, L' said single negative lens 1J said two biconvex lens members 15", L',, said meniscus-shaped lens member L'-,, said biconcave lens member L, and said other biconvex lens member L',, based upon a value of unity for the minimum overall focal length, their refractive indices 11,, and their Abbe numbers v, are substantially as given in the following table:

-continued Thicknesses Lcnses Rudu and Separahons n, v

11,. 0.144 d 0420 254 ll 

1. A varifocal objective consisting of a fixed positive front component, an axially shiftable negative intermediate component and a fixed positive rear component; said front component consisting of a biconcave first lens, a biconvex second lens, and a nearly planoconvex third lens closely spaced from said second lens, said first lens being separated from said second lens by an air space close to half the axial length of said front component; said intermediate component being a single negative lens; said rear component consisting, from front to rear, of two biconvex positive lens members, a meniscus-shaped positive lens member, a biconcave lens member and another biconvex lens member; the individual focal lengths of said front component, said intermediate component and said rear component being approximately related in the ratio +5.5 : -2.5 : +1, the relative positioning of said components being such as to provide an image diagonal which is shorter than the separation of said first and second lenses.
 2. A varifocal objective as defined in claim 1 wherein said positive lens members are singlets.
 3. A varifocal objective as defined in claim 1 wherein the numerical values of the radii r1 - r19 and of the thicknesses and separations d1 - d18 of said first, second and third lenses L1, L2, L3, said single negative lens L4, said two biconvex lens members L5, L6, said meniscus-shaped lens member L7, two cemented lenses L8, L9 constituting said biconcave lens member, and said other biconvex lens member L10, based upon a value of unity for the minimum overall focal length, their refractive indices nd and their Abbe numbers Nu d Are substantially as given in the following table:
 4. A varifocal objective as defined in claim 1 wherein the numerical values of the radii r1 - r19 and of the thicknesses and separations d1 - d18 of said first, second and third lenses L1, L2, L3, said single negative lens L4, said two biconvex lens members L5, L6, said meniscus-shaped lens member L7, two cemented lenses L8, L9 constituting said biconcave lens member, and said other biconvex lens member L10, based upon a value of unity for the minimum overall focal length, their refractive indices nd and their Abbe numbers Nu d are substantially as given in the following table:
 5. A varifocal objective as defined in claim 1, wherein the numerical values of the radii r''1 - r''18 and of the thicknesses and separations d''1 - d''17 of said first, second and third lenses L''1, L''2, L''3, said single negative lens L''4, said two biconvex lens members L''5, L''6, said meniscus-shaped lens member L''7, said biconcave lens member L''8 and said other biconvex lens member L''9, based upon a value of unity for the minimum overall focal length, their refractive indices nd and their Abbe numbers Nu d are substantially as given in the following table: 